1. Field of the Invention
The present invention relates to an optical information recording and reproducing apparatus, and a recording and reproducing method used in the apparatus. More particularly, the present invention relates to an optical information recording and reproducing apparatus for recording and reproducing a compressed and encoded video signal, and a recording and reproducing method used in the apparatus.
2. Description of the Related Art
The image data for a moving picture includes an enormous amount of information as compared with the data for a still picture, so that it is very difficult to record or reproduce the image data for a moving picture by a real-time processing. Accordingly, digitized image data is coded and compressed to a degree at which the deterioration of information is negligible with respect to the original image, and then recorded on a recording medium. Due to the data compression and coding, image data can be recorded onto the recording medium for a longer time period and image data can be reproduced from the recording medium for a longer time period.
As the coding methods for As image date, there are intra-frame (or intra-field) coding and inter-frame (or inter-field) coding. In the intra-frame (or intra-field) coding, the coding is performed within a frame (or a field). In the inter-frame (or inter-field) coding, the coding is performed between frames (or between fields). Hereinafter, the description is made for the case of frames, but it is appreciated that the same description can be made for the case of fields.
In general, some frames are included in one group. In the group, data of at least one frame is processed by intra-frame coding which has relatively low compressibility. In each group, a frame compressed by the intra-frame coding is referred to as an I frame. For the remaining frames in the group, the inter-frame coding which has relatively high compressibility is performed. By combining the intra-frame coding with the inter-frame coding, it is possible to comparatively suppress the deterioration of information, and to improve the compressibility.
The coded and compressed data is recorded onto the recording medium in the following manner. First, the data compressed by intra-frame coding (I-frame data) and the data compressed by inter-frame forward predictive coding (P) or inter-frame bidirectional predictive coding (B) are arranged along a time axis, and various codes are added, so as to constitute a unit of data. Then, the unit of data is divided into sectors each having a fixed data capacity. The sectors are provided with respective addresses, and the data is recorded onto the recording medium. When the image data which has been thus recorded onto the recording medium is to be reproduced, the reproduction is performed while recognizing the address of the sector.
However, in the case where only the intraframe coded and compressed data is to be reproduced in a trick play such as a high-speed reproduction, the above-described recording and reproducing method requires a table indicating the relationship between a sector address and data recorded in the sector. The table must be recorded in an area of the recording medium other than the area in which the coded data is recorded. For example, when image data is to be recorded onto an optical disk, sector addresses of I-frame data are recorded in a management area provided on the inner side of the optical disk (FIG. 11). The sector address cannot be written during the recording of the coded data so that it must be recorded after the recording of the coded data. This may result in a problem in that, if for some reason the table indicating the relationship cannot be written, a trick play cannot be performed.
In the cases where the image data is recorded after being coded and compressed, it is necessary to expand and decode the data for reproducing it. Therefore, it has been proposed that programing data for decoding used in the reproduction be recorded in header portions of respective data (grouped data) coded by different coding methods (for example, described in Japanese Laid-Open Patent Publication No. 2-123883). However, in such a conventional method, the information amount of the image data is not known until the compressed image data is expanded/decoded by a decoder and the codes are analyzed. Therefore, in the cases where data of different transfer rates are mixedly recorded in one recording medium, there arises a problem in that the buffer memory may cause overflow or underflow during the reproduction, or the data processing in the decoder may be delayed.